3 Mutations in Dna Lac operon DNA repair DNA/RNA/protein synthesis Start and stop codons Functional organization of a eukaryotic gene Regulation of gene expression Flashcards
Rank the following types of mutations from most to least severe: missense, frameshift, silent, and nonsense.
Frameshift > nonsense (a stop codon) > missense > silent
What type of DNA mutation results in no change to the amino acid that is being coded for?
Silent mutation
Silent mutations are often the result of changes in what position of a codon?
Missense mutation—the severity of the mutation depends on the location of the change
What type of DNA mutation results in the misreading of all downstream nucleotides? Why does this happen?
Frameshift mutation; deletion or insertion of a number of nucleotides not divisible by 3 shifts the reading frame
What kind of protein usually results from a frameshift mutation? Give an example of a disease resulting from this type of mutation.
A truncated and nonfunctional protein; Duchenne muscular dystrophy
A lab detects a mutation: ACTCCTGAGGAG to ACTCCTGTGGAG. Protein size is unchanged; the protein is nonfunctional. Identify the mutation type.
This is likely a missense mutation (GAG to GTG = glutamate to valine)
A mutation causes a guanine to replace an adenine. This is a ____ (transition/transversion).
Transition (purine to purine or pyrimidine to pyrimidine)
A mutation causes a guanine to replace a thymine. This is a ____ (transition/transversion).
Transversion (purine to pyrimidine or vice versa)
A patient tests positive for a hemoglobin-related disease caused by a missense mutation. What is the disease?
Sickle cell disease
What happens to Escherichia coli in the absence of glucose and the presence of lactose?
The lac operon is activated; a switch to lactose metabolism occurs
Lac operon genes are strongly expressed when there is a ____ (high/low) level of glucose and lactose is ____ (available/unavailable).
Low; available
Escherichia coli is grown in the lab. Are lac operon genes strongly or not strongly expressed in case of low glucose and available lactose?
Strongly expressed.
Are lac operon genes strongly or not strongly expressed in case of low glucose and low lactose? How about high glucose and low lactose?
No, not expressed; no, not expressed. Very low basal expression
During nucleotide excision DNA repair, which enzyme removes the damaged DNA?
Endonuclease
A 2-y/o child must stay inside during the day because sunlight causes dry skin and sunburn. By what mechanism does this disease work?
A defect in nucleotide excision repair that prevents repair of thymidine dimers (xeroderma pigmentosum)
What is the first step in the base excision repair of damaged DNA?
Glycosylases recognize and remove a single damaged base
In base excision repair, what do the apurinic/apyrimidinic endonucleases do?
They cut the DNA at apurinic and apyrimidinic sites and remove the empty sugar
In single-strand DNA repair, how do nucleotide excision and base excision repair differ?
Nucleotide excision removes the entire nucleotide structure, and base excision repair removes bases without disturbing the DNA backbone
What type of DNA repair is important in spontaneous/toxic deamination?
Base excision repair
A patient lacks the ability to carry out nonhomologous end joining in DNA. What disease does the patient have?
Ataxia telangiectasia, a failure of nonhomologous end joining (bringing together of DNA fragment ends to repair double-stranded breaks)
Which method of DNA repair repairs double-stranded breaks? What two conditions are associated with it?
Nonhomologous end joining; ataxia telangiectasia and Fanconi anemia
A patient is found to have hereditary nonpolyposis colorectal cancer (HNPCC). What process is defective? How does it occur normally?
Mismatch repair; recognition of newly synthesized strand, removal of mismatched nucleotides, and filling and resealing of the gap
A patient has xeroderma pigmentosum. What process is defective? How does this process occur normally?
Nucleotide excision repair; specific endonucleases release damaged bases, and DNA polymerase and ligase fill and reseal the gap
How does the process of repair of spontaneous/toxic deamination work normally?
Nucleotide removal (5′-end cleaved), lyase cleaving of 3′-end, gap filling with DNA polymerase-β, sealing with DNA ligase
